Low-Dimensional Copper(II) Complexes with the Trinucleating Ligand 2,4,6-Tris(di-2-pyridylamine)-1,3,5-triazine: Synthesis, Crystal Structures, and Magnetic Properties^†

The preparation and structural characterization of three new copper(II) complexes of formula [Cu3(dipyatriz)2(H2O)3](ClO4)6·2H2O (1), {[Cu4(dipyatriz)2(H2O)2(NO3)2(ox)2](NO3)2·2H2O}n (2), and [Cu6(dipyatriz)2(H2O)9(NO3)3(ox)3](NO3)3·4H2O (3) [dipyatriz = 2,4,6-tris(di-2-pyridylamine)-1,3,5-triazine and ox = oxalate] are reported. The structure of 1 consists of trinuclear units [Cu3(dipyatriz)2(H2O)3]6+ and uncoordinated perchlorate anions. The two dipyatriz molecules in 1 act as tris-bidentate ligands with the triazine cores being in a quasi eclipsed conformation. Each copper atom in 1 exhibits a distorted square pyramidal geometry CuN4O with four pyridyl-nitrogen atoms from two dipyatriz ligands building the basal plane and a water molecule occupying the axial position. The values of the intratrimer copper−copper separation are 8.0755(6) and 8.3598(8) Å. Compound 2 exhibits a layered structure of copper(II) ions which are connected through bis-bidentate dipyatriz ligands and bidentate/outer monodentate oxalato groups. The copper atoms in 2 exhibit six- [Cu(1)N4O2] and five-coordination [Cu(2)N2O3]. A water molecule and three pyridyl-nitrogen atoms [Cu(1)] and two pyridyl-nitrogen plus two oxalate-oxygen atoms [Cu(2)] define the equatorial plane whereas either an oxalate-oxygen and a pyridyl-nitrogen [Cu(1)] or a nitrate-oxygen [Cu(2)] fill the axial positions. The copper−copper separation through the bridging oxalato is 5.6091(6) Å whereas those across dipyatriz vary in the range 7.801(1)−9.079(1) Å. The structure of compound 3 contains discrete cage-like hexacopper(II) units [Cu6(dipyatriz)2(H2O)9(NO3)3(ox)3]3+ where two trinuclear [Cu3(dipyatriz)]6+ fragments are connected by three bis-bidentate oxalate ligands, the charge being balanced by three non-coordinated nitrate anions. The values of the intracage copper−copper distance are 5.112(3)−5.149(2) Å (across oxalato) and 7.476(2)−8.098(2) Å (through dipyatriz). Magnetic susceptibility measurements of polycrystalline samples of 1−3 in the temperature range 1.9−295 K show the occurrence of a weak antiferromagnetic interaction across dipyatriz in 1 [J = −0.08(1) cm−1, the Hamiltonian being defined as ∧H = −J (∧S1·∧S2 + ∧S1·∧S3 + ∧S2·∧S3)] and weak ferro- (2) and strong antiferromagnetic (3) interactions through the oxalato bridge in 2 [J = +0.45(2) cm−1] and 3 [J = −390(1) cm−1]. The use of the dipyatriz-containing copper(II) species as a building block to design homo- and heterometallic magnetic compounds is analyzed and discussed.